1. Field of the Invention
This invention relates to voltage detection circuits and, more particularly, to the detection of direct current voltages in the presence of interfering alternating current signals.
2. Description of the Prior Art
It has been the practice to detect particular levels of direct current voltage by simple threshold responsive circuits. If alternating current components were present which might interfere with the proper detection of the direct current voltage threshold, it was common to provide alternating current filter circuits of lesser or greater complexity. It is necessary to reduce the alternating current components to a sufficiently low amplitude level so as to avoid any substantial interference with the direct current voltage detection. Unfortunately, however, such filter circuits are normally composed of discrete components. Indeed, even simple filters, such as resistive-capacitive filters, required a capacitor which had to be realized as a discrete component. Such discrete components are large, bulky, expensive to provide and are incompatible with modern integrated circuit technology. This problem is aggravated with more complex filters requiring inductive as well as capacitive elements and requiring a larger number of such elements.
On the other hand, digital logic circuitry which can be realized in integrated circuit form has become smaller, more compact and less expensive as integrated circuit technology has improved. In fact, it has come to the point in certain types of design where fairly complex logical circuitry can be economically substituted for simple, discrete current components. This tendency has led to the digital filter technology and is likely to continue on into the foreseeable future. Unfortunately, up to the present time, analog voltage detection has not been able to obtain the benefits of such integrated circuit technology.